Telephone system



Jan. 14, 1930. RAY 1,744,013

TELEPHONE SYSTEM f/G. g. 1926 4 Sheets-Sheet 1 cza- Jan. 14, 1930. A. J. RAY 1,744,013

TELEPHONE SYSTEH Filed Aug. 9, 1926 4 Sheets-Sheet 2 BUSY TONE.

Jan. 14, 1930. A. J. RAY

TELEPHONE SYSTEI Filed Aug. 9, 1926 4 Sheets-Sheet 3 RING!" G- LEA D 1m 1' Jag i v HTThLl .1511. 14, 1930. A. J. RAY

I TELEPHONE SYSTEM File Aug- 1926 4 Sheets-Sheet 4' BUSY TONE Patented Jan. 14, 1930 UNITED STATES ARTHUR JAY BAY, OF LIVERPOOL, ENGLAND, ASSIGNOR, BY MESNE ASSIGNMENTS, T ASSOCIATED TELEPHONE 81; TELEGRAPH COMPANY, 013 KANSAS CITY, MISSOURI TELEPHONE SYSTEM Applicationa'filedi August 8, 1926,. Serial No. 128,047, and in Great Britain October 13, 1925.

The present invention relates to telephone systems and is more particularly concerned with systems in which battery for speaking purposes is supplied in the direction or the called party, that is to say, it is supplied: from the first numerical switch in the exchange or in. the caseoi? an inter-exchange call, from the first switch of the train in each exchange. The invention moreover is particularly applicable to a system: in which battery for dialling purposes is fed forward from the first numerical. switch in an exchange so that the impulse responding relay in any subsequent switch is bridged directly across the speaking 5 leads without battery or earth connections,

and the invention may there-fore be considered an: improvement in or modification of the arrangement shown in United States application Serial No. 7 14,2 10, filed May 19th 192%, which corresponds to British Patent The object of the invention is to modify the arrangement above referred to: in such a manner that supervision is effected over the '25 speaking leads separately rather than by the alteration of the resistance 01' the loop circuit. This arrangement is found in practice to give improved operating conditions, and

also enables a number of simplifications to be made in the circuits. The main feature of the invention is that in an automatic or semiautomatic telephone system, battery and earth are fed forwards over'the two: speaking leads respectively and a plurality of super- 'visory relays are connected to one load only during both dialling and speaking.

The invention will be better understood from the following description of one method of carrying it into effect which should be 411 taken in conjunction with the accompanying drawings. It will be understood however that the arrangement shown isby way of example only and that various modifications in the circuit details could be made by those skilled' in the art without departing from the spirit of the invention.

Reiterring now to the accompanying drawings, Fig. I shows by the usual diagrams the circuits of an improved first selector; Fig. 2,

these or an incoming selector; Fig. 3, those diiiers in certain respects from the first selector taken into use by a calling subscriber. Calling and called automatic subscribers stations are not shown, but these it will be understood may be of any suitable type, preferabl y having individual rotary line switches =5;

associated with them. It may be mentioned also that the circuits shown in Figs. 3 and 4 for the intermediate selector and connector are substantially the same as those disclosed in the main patent. All the switches are assumed to be mechanically of the two-directional type arranged first to raise their wipers opposite a selected level and then to rotate over the contacts in that level.

A complete connection will first be traced between two automatic subseril'iers it being assumed for convenience oil description that a 100,000 line system is under consideration so that 5 digits are necessary to set up a complete call. When the calling subscriber removes his receiver, his rotary line switch seizes a first selector, for instance that shown in l, and when switching through takes place, a circuit is completed over conductors 1 and 2 and the subscribers loop for line relay 5, which accordingly operates, and at armature 6 completes a circuit for relay 8 which operates also. At armature 9 earth is connected to. the release earth conductor 3 to maintain the line switch operated, at armature 1Q the impulsing circuit is prepared and at armature 11 a circuit is completed which extends over armature a6 and its back contact, winding of relay 21 to battery. Relay 21 thereupon operates, at armatures 22 and 27 disconnects one terminal of the condensers in the speaking leads, so as to prevent these condensers having an adverse effect on the impulsing, at armature 23 opens a point in the metering circuit, at armature 24 opens a point in the circuit for short-circuitii'ig the upper winding of relay 28, at arn'iature 25 prepares a locking circuit for itself, and at armature 26 opens a pointin the locking circuit for relay 28.

The switch is now in a condition to respond to dialled impulses, and when the subscriber transmits the first digit, a corresponding number of interruptions are produced in the circuit of relay 5, which de-energizes accordingly. Upon each release of armature 6, a circuit is completed which extends over the back contact of this armature, armature 10 and its front contact, winding of relay 13 to battery, and parallel thereto, over armature 48 and its back contact, winding of vertical magnet 20 to battery. Magnet 20 accordingly operates to raise the switch shaft and wipers a number of steps corresponding to the digit dialled, and relay 13 also energizes and being slow, remains operated throughout the train of impulses. Relay 13 at armature 14 connects dead earth to the upper speaking lead, and at armature 17 short-circuits the retard 18; these operations are however without effect at this time. luoreover at armature 15 it prepares a circuit for the stepping relay 36, which is completed as soon as off-normal contacts 39 close on the first step of the switch, this circuit extending as follows: earth, front contact and armature 9, armature 15 and its front contact, armature 44 and its back contact, interrupter springs 41, off-normal springs 39, winding of relay 36 to battery. Relay 36 upon operating, at armature 37 prepares a circuit for rotary magnet 40 and at armature 38 completes a locking circuit for itself. Vhen relay 13 'de-energizes on the termination of the train of impulses, a circuit is completed for magnet 40, and this accordingly operates to rotate the switch wipers one step. at the same time towards the end of its stroke opening the interrupter springs 41. 'lhereupon the circuit of relay 36 is opened and it de-encrgizes thus opening the circuit of magnet 40 which de-energizes also.

In case the trunk extending from the confacts with which the wipers are now in engagement is busy, earth will be present on the test contact engaged by wiper 53 and a circuit will then be completed for stepping relay 36, which again effects the operation of the rotary magnet and is then de-energized. This alternate operation of magnet 40 and relay 36 continues until wiper 53 no longer finds earth. whereupon relay 42, which has previously been short-circuited, energizes in series with relay 36, the latter however not being now energized owing to the high resistance of relay 42. Relay 42 at armature 44 extends earth forward to wiper 53. at arn1ature 45 opens a point in the locking circuit of relay 36, at armature 46 opens the initial energizing circuit of relay 21. at armature 47 extinguishes the lamp 50, and at armature 48 opens a point in the circuit of vertical magnet 20 so as to prevent this magnet being again operated by subsequent trains of impulses. Moreover-at armatures 43 and49,the speaking leads are switched through, \YlICICUjOil a circuit is completed as follows: battery, retard 18, armature 7 and its front contact, armature 49 and its front contact, wiper 52, contact 62, winding of relay 63, normally closed s i ings controlled by armature 78 to earth. llciay 63 thereupon operates and at armature 64 completes a circuit for relay 66. This relay at armature 67 connects up a holding earth for various subsequent operations, at armature 68 prepares the impulsing circuit, and at armature 69 completes a circuit for relay 77 which extends over armature 102 and its back contact. Upon the operation of relay 77, at armature 78 relay 63 is connected directly across the speaking conductors, and its circuit then extends over contact 61, wiper 51, front contact and armature 43, winding of relay 33, upper winding of relay 28 to earth. Both relays 28 and 33 operate in this circuit, and the former at armature 31 completes a locking circuit for relay 21. It will be understood that since relay 21 is slow to release, this locking circuit is completed before it has had time to fall away in response to the opening of its initial energizing circuit at armature 46. Relay 77 in the incoming selector furthermore, at armature 8O prepares a lockin; circuit for itself, at armature 81 opens a point in the locking circuit of relay 84, and at armatures 82 and 83 disconnects the condensers in the speaking leads so as to prevent their interfering with the proper transmissi on of impulses.

The subscriber will now dial the second digit in the wanted number, whereupon as before a numher'of interruptions are produced in the circuit of line relay 5. Owing to the intermittent release of armature 6. relay 13 is again operated, and at armature 14 it short-circuits relays 28 and 33, at armature 16 closes an alternative locking circuit for relay 21 so as to prevent this relay releasing when its previous locking circuit is opened owing to the release of relay 28, and at armature 17 short-circuits retard 18. The impulses received by relay 5 are repeated at armature 7 to line relay 63 of the incoming selector, which accordingly (lo-energizes correspondingly. Thereupon at armature 64 impulses are transmitted to vertical magnet 94 and relay 72, the latter being energized throughout the train of impulses, and at armature 74 serving to complete a circuit for stepping relay 95. Armature of line relay 63 is without effect at this time but it serves subsequently to repeat impulses to succeeding switches. Similarly the operation of armature 73, 75 and 76 of relay 72 is at present without effect, since these armatures only perform useful functions after the incoming and at armature: 7 1 initiates the hunting op- GltttlOIl. Thlstavlresplacc owing to theinteraction of relay and magnet 93 in themannor described in connection with the first selector, Fig. 1. hen a freetrunlc extend-- ing to a succeeding: switch is found as repre sented by the absence'of earth on thetest contact encountered by wiper 106 ,.rela-y98 is no longer short-circuited and energizes, thereupon at armatures 99 and 10 1 connecting up: the wipers, at armature 100 feeding. earth forward over wiper 106 and at armature 102 opening, the initial: circuit of relay 77. The connection: is new extended it will be assumed to the intermediate selector shown in Fig. 3, and accordingly a circuit including relays 8 1 and 89' in series is completed for the line relay 1141 of the-intermediateselector over armatures 13 1: and 138 and their back C0111- tacts. The only useful: function performed by relays 84: and: 89* upon energi ing at this time isthe completion of a locking, circuit for maintaining relay 77 operated. Upon the operation of. relay 11 1-, a circuit is preparec at armature 116 for short-circuiting relay 117, while at armature the energizing circuit of this relay is completed. as follows: earth, trout contact and. armature 67 front contact and armature 100, wn' per 106, contact 1113, back contact and armature 135, armature 115 and its front contact, winding of relay 117, resistance 121 tobattery. Relay 117 upon operating, at armature 118 completes a lochingcircuit for itselt independent of armature 115, at. armature.- 119/ prepares the circuit for the vertical magnet 122, and. at armature 120 prepares a circuit for the stepping relay 128.

When the third digit is dialled, the impulses are repeated by relays 5 and 63- to relay 114, relays 13 and 72 being energized throughout the train of impulses and serving to provide improved impulsing conditions as well as to maintain relays 21 and. 77 energized. Upon each de-energization of relay 11 1, a circuit is completed from earth, back contact and armature 137, armature 116 and its back con tact, armature119 and its frontcontact, vertical magnet 122 to battery so that the. switch is stepped up to the required level in known manner. Relay 128-is energized assoon as of.- normal contacts 127 are closed and after contacts c1ose, which also takes place on the first step" of the switch, relay 117 is shortcircuited. each time armature. 116 engages its '5 front contact thishowever isnot sufficient to cause it to release during a train of impulses. Upon the termination of the train. of impulses however, relay 117 remains short-circuited and accordingly releases. after a short interval, thereupon at the normally closed.

springs controlled. by armature 120 completing a circuit for the rotary magnet 131 by the operation of which the switch wipers are rotated into engagement with the first set of bank contacts in the selected level. The hunting operation of the switch then takes place in a manner similar to that above described owing to the oint action of stepping relay 128 and rotary magnet 1'31. lVhen a tree trunk extending to a succeeding; switch is found, switching relay 123 operates and at armatures 13 1 and 138 connects the speaking leads through, at the same time opening the circuit of relay 114, at armature 135 opens. a point in the circuit of relay 117,.at armature 136 feeds earth forward to test wiper 141, and. at armature 137 opens a point in the circuit of the release magnet 123. The connection is now extended to a connector, for instancetlrat shown in Fig. 41, and accordingly the following circuit is completed: battery retard 70, armature 65 and its front contact, armature: 10 1 and its front contact, wiper 107, contact 112, armature 138 and its front. contact, wiper 1 10, contact .152, off-normal springs167, winch ing of relay 155, back contact and armature 185, contact 151,.wiper 139, front contact and armature 13 1-, contact 111, wiper 165, front contact and armature 99, upper winding of relay 8 1, winding of relay 89 to earth. Re lays 8 1 and 89 are again operated inthis circuit, and relay also operates, and thereby at armature 156 prepares a circuit for relay 158. Moreover on the operation of relay 132 earth is extended over wiper 1e11, contact 153', off-normal. springs 168,.lower winding or relay 169 to battery. Upon. opera-ting, relay 169 at armatures 170. and 174: opens points in the ringing circuit, though this is without effect at the present time, at armature-.172 prspares a locking circuit for itself, at armature 173 connects up the vertical magnet 165, and at armature 171 completesthe circuit for relay 158 from the release trunk conductor. Relay 158 thereupon operates, at arnaatures 159 and 160 completes a locking circuit. for itself, at armature 161 closes a point in the impulsing circuit, and. at armature 162. shortcircuits off-norm al' springs 167 so as to maintain the circuit of relay 155 after the off-non inal springs open when the switch takes the first step,

hen the subscriber dials the next series of impulses, interruptions are prodi-iced before, and are repeated at the first and in coming selectors so as to bring about the intermittent dc-energization oi: relay 155. Each time this relay releases, it completes-a circuit at armature 157 for the vertical magnet so that the switch is stepped up the required number of steps. Relay 175, which arranged to be slow torelease, is energized in parallel with the vertical magnet, and at armature 178 completes the locking circuit for relay 169,, so that this relay remains energized during the train of'im-pulses in spite of the opening of its initial energiring circuit at.

off-normal springs 168. At the end of the train of impulses however, relay 175 falls away and consequently relay 169 also, and the impulsing circuit is then altered so that the next series of impulses are transmitted to rotary magnet 164 instead of vertical magnet 165. During the transmission of this final series of impulses, relay 175 is again energized and at armature 177 connects the busy relay to test wiper 195 and at armature 176 shunts armature 180 so as to maintain the circuit of relay 158 in case busy relay 179 is energized owing to the wipers passing over busy contacts.

Assume in the first instance that the wanted line is idl when the switch wipers come to rest in engagement with the contacts thereof. In this case busy relay 179 will not be operated, and when relay 175 deenergizes shortly afterwards, a circuit will be completed as follows: from earth on the release trunk conductor, armature 181 and its back contact, upper winding of switch ing relay 183, back contact and armature 177, test wiper 195 and by way of the switching relay and rotary magnet of the called partys line switch to battery. The switching relay of the line switch and relay 183 operate in series in this circuit and the former in known manner clears the called line of its normal battery and earth connections. Relay 183 at armatures 184 and 190 completes the ringing circuit, at armature 185 connects up the small condenser 191 so as to give the calling party ringing induction, at the same time opening the circuit of relay 155, at armature 186 opens the circuit of relay 158, at armature 187 completes a locking circuit for itself by way of its lower winding, at armature 188 connects direct earth to test wiper 195 and at armature 189 prepares a locking circuit for relay 169. Ringing current is now sent out from the generator over lead 154 and by way of the upper winding of relay 169 to ring the wanted partys bell.

The operation of armature 183 also opens the circuit of relays 84 and 89 in the incoming selector, consequently both these relays de-energize and the former at armature 87 opens the locking circuit of relay 77 so that this relay also tie-energizes. Thereupon at armature 78 the circuit of the relays 28 and 33 in the first selector is opened and these deenergize, thereby in their turn opening the circuit of line relay 21. It will be noted however that relay 63 is now connected to earth in the incoming selector and accordingly remains energized over the lower talking conductor in spite of the cessation of current flow over the upper talking conductor. Moreover since, as previously mentioned, relay 21 is slow to release, armature 29 will leave its front contact before armature 23 en ages its back contact, and there is thus no anger of the metering circuit being completed prematurely. Similar considerations apply to the supervisory circuit in the incoming selector.

The circuits remain in this condition until the calling party replies, whereupon a di rect current bridge is completed across the speaking leads, and the ringing trip relay 169 is then operated, thereupon at armatures 170 and 174 cutting oil? the ringing and connecting the speaking leads through, and at armature 172 completing a locking circuit for it self. A circuit is now completed for relays 84 and 89 in series with the called partys loop and the retard 7 0. Since it is assumed that the connection has been extended to another automatic subscriber, the current flow in this circuit will be suilicient to operate both relays 84 and 89. The latter at armature 90 connects up the retard 92 to the upper trunk conductor extending back to the first selector, while relay 84 at armature 88 completes a locking circuit for itself by way of its lower winding, at armature 86 shortcircuits its upper winding so as to give properly balanced speaking conditions, and at armature 85 short-circuits the high resistance 108. A circuit is now completed for relays 28 and 33, and owing to the short-circuiting of resistance 108, both these relays are able to operate. The operation of relay 33 is without effect in these circumstances, but relay 28 at armature 29 completes the metering circuit over conductor 4, at armature 30 short-circuits its upper winding and at armature 32 completes a locking circuit over its lower winding.

The connection has now been completely set up and the subscribers may converse as desired, and when they have finished they will replace their receivers. Assuming that the called party replaces his receiver first, it will be seen that the circuit for relay 89 is opened and this relay accordingly de-energizes, thereby opening the circuit of relay 33, which de-energizes also. The connection is still held up however until the calling party replaces his receiver, and when he does so relay 5 is de-energized, and at armature 7 opens the circuit of relay 63 in the incoming selector, and at armature 6 opens the circuit of relay 8. Upon the de-energization of relay 8, earth is removed from the release trunk conductor, whereupon the subscribers line switch and the first selector are restored to normal, the latter by the operation of release magnet 19 over oii-normal contacts 12. The release of relay 63 opens the circuit of relay 66 at armature 64, and when this relay falls away, earth is removed from the release trunk conductor at armature 67, whereupon relays 98,132, 169 and 183 are released and the incoming selector, intermediate selector and connector are restored to normal by the operation of their respective release magnets 71, 123 and 163. It

may be mentioned that the contact 12 1 on magnet 123 is provided in order to prevent the operation of the rotary magnet 131 in case the test wiper should engage busy contacts in restoring to normal. The whole connection has'now been released and all the apparatus employed :may be used for setting up other connections.

Suppose now that the wanted party was busy when called, in this-case when :the wipers 193 195 came to rest in engagement with his line, wiper 195 would find earth, and consequently relay 179 would il36 energized, thereby at armature 181 preparing -a locking circuit for itself,and at armature 182.connecting up busy tone and intermittent battery through a high resistance over lead 192. When relay 175 falls away an instant later, the locking circuit for relay 179 is completed at the normally closed springs controlled by armature 177 and moreover at armature 176 the circuit of relay 158 is opened, whereupon relay 158 releases its armature 162, thus opening the circuit of relay 155. This has the effect, as in the caseof a successfulcall, of opening the circuit of relays 84; and 89 and they fall away as before. They arenow supplied however with intermittent battery througha liigh resistance over lead 192, and

during the period that this battery is applied relay 89 operates, thereupon at armature 90 connecting .up retard 92, but in this case throughresistance 108 since relay 84 is unable to operate A similar change is therefore brought about at the first selector, that is to say, relay33enegizes intermittently but relay 28 is unabletodo so sothat no metering takes place. In thiscase the operation of relay 33 is without effect since the connection has been set up'by a su'bscribenbuthe receives thebusy tone through the various condensers in the talking circuit. He accordingly hangs up and relay 5 is then ole-energized and the'connection is released in the manner just described.

It should be mentionedatthis point thatin case any of the selectors used in setting-up the connection should be rotated to the 11th position owing to all trunks in the desired level being busy, the appropriate switching relay would be operated but since the wipers are then disconnected, no maintaining circuit would be completed for therelay such as'28 or 84: and hence the relay such as 21 or 77 would de-energize and effect the change from impulsing to supervisory conditions so as to permit of the busy signal being transmitted back. Moreover "the cam springs indicated at 54, 108 and 142 in Figs. 1, 2 and 3 respectively are operated and busy tone and intermittent battery through a highresistance are connected to the upper speaking conductor. Inasmuch however as the first selector, Fig. 1, will not be taken into use from an operators position, only busy tone need be connected up ;at springs 54:, since it is not necessary to make provision for flashing an operators supervisory lamp.

, onsider now the case in which a call is extended by an automatic subscriber to an operatorsrposition, forinstance for information oriior-initiatingatoll call. Fort-his purpose it will zbelassumed-for convenience of descriptionthat the firstselector in Fig. 1 has access 011 certain level, for instance the tenth, .to apparatus such as is shown in Fig. 5. Hence when asubscriber dials'the requisite idigit for obtaining access .to the operator, the first ,selectorin Fig. 1 isstepped up in the usual manner and then hunts over the selected level. then a tree trunk .is foundswitching relay 42 operates=withsubstantially theresults previously described A circuit is now completed from battery, retard 18, armature 7 and its front contact, armature 49 and its frontcontact, wiper 52, contact 202, winding of relay .203 to battery. It will be noticed however that no circuit is completed at This time iorirelays 28 and 33,;and consequently when the circuitlof relay :21 isopenedat armature .46, :it tie-energizes andthereby establishes supervisory conditions as above described. Relay .203 operates in the above tracedcircuit andat armature 205 completes a circuit forithecalling lamp 212, and at armature 201 connects np ringing induction over :the lead 210 so as :to notify the calling party asnsual-that theattention of the-wanted party is being attracted. The :operator, upon noting the lighted condition of the lamp 212, inserts the plug ota cord circuit such as that shown into the jack associated with lamp 212, thereupon completing a circuit forthe sleeve relays 206 and2l15insenies. Both these relays operate and the latter-atarmature-216lights-the supervisory lamp 217 in the cord circuit. Re'layQOG upon operating, at armature 208 cuts oil the ringing tone,-and connects the retard 211 across the jack springs at armature 209 extinguishes the calling lamp 212 and at armature 207 connects battery through the retard 213 "by way 01 a high resistance 214 to the upper trunk conductor. A circuit is then completed for relays 28 andi33, but owing to the inclusion of resistance 214 in thecircu'it, only relay 33 can operate,and consequently no metering takes place. The operation oi relay 33 completes an auxiliary holding circuit for the relay 8 at armature 35, which circuit extends from earth, armature 9 and its front contact, ,armature 32 and its back contact, front contact and armature 35 to therelay .8. This comprises the operators holdup feature by meansof which-therelease ofthe connection is removed from the controlof the calling party and placed under the .operators control. It should be mentionedthat relay 218 in the'cord circuit is operated when the plug is inserted'under the conditions assumed,-and

at armature 219 opens the circuit of the lamp 217.

The subscriber may now make his enquiry and when he has obtained the necessary information, he will replace his receiver, whereupon relay 5 will de-energize and open the initial circuit of relay 8. Owing to the auxiliary holding circuit previously traced however, relay 8 does not (lo-energize at this time, and consequently the connection is not yet released. Relay 5 however at armature 7 opens the circuit for relay 203, and this consequently de-energizes, thereby opening the circuit of relay 218 in the cord circuit. Upon the de-energization of relay 218, the supervisory lamp is lighted at armature 219 and the operator then knows that she may take down the connection. \Vhen this is done, battery is removed from the upper speaking conductor, consequently relay ole-energizes and subsequently relay 8, and the first selector and line switch are restored to normal in the usual manner.

One further case has to be considered, namely, that in which connections between manual subscribers and automatic subscribers are set up by the A operator, who is provided with a dial for this purpose. For reasons which will appear subsequently, the operators first selector differs in several details from the first selector used by automatic subscribers, and the operation of this selector will be briefly traced, reference being had to Figs. 6 and 7.

\Vhen the receiver is removed at the calling substation depicted on the left of Fig. 6, the associated line relay is operated and the calling lamp is lighted to attract the attention of the operator. She accordingly inserts the answering plug P into the multiple jack J thereupon operating the cut-off relay to remove the normal battery and earth connections from the calling line. She then operates her speaking key which is not shown, and ascertains the calling partys requirements, after which she inserts the calling plug P into a jack J 2 associated with a tree trunk line leading in the required direction. The operator then throws the dialling key K and sets up the connection by manipulating the dial in the proper manner. It will be seen that when plug P is inserted in the jack J a circuit is completed from earth, winding of relay 257, sleeve of jack, sleeve of plug, lamp 256, to battery, and accordingly the lamp lights and the relay operates, thereby lighting also the lamp 259 to indicate that the trunk is busy. Moreover a circuit is now completed as follows: battery, retard 253, lower right-hand winding of the repeating coil, normally closed springs of the key K, ring contacts of the plug and jack, conductor 261, winding of relay 271, normally closed springs controlled by armature 285 to earth. Relay 271 operates in this circuit and at armature 272 completes a circuit for relay 274 and this at armature 275 connects up a locking and holding earth, at armature 276 prepares the impulsing circuit, and at armature 277 completes a circuit by way of armature 299 and its back contact for relay 283. Relay 283 upon operating in its turn, at armatures 284 and 287 disconnects the talking condensers and at armature 285 connects relay 271 across the two speaking leads. It will be noted that the operation of relay 254, which would give a false indication on the lamp 256, is prevented at this time as it is short-circuited by the oil-normal springs 308.

The operator now throws the dialling key K, thereby cutting out both retard 253 and relay 254 and then by operating the dial opens the springs 252 momentarily the required number of times. Each time the circuit of relay 271 is opened, it de-energizes and in the usual manner efi'ects the operation of vertical ma gnet 290. Relay 278 is energized throughout the train of impulses and at armature 280 controls the starting of hunting operation which takes place owing to the interaction of: stepping relay 292 and rotary magnet 291. hen wiper 307 no longer finds earth, switching relay 295 operates and switches the connection through in the manner above described. Succeeding trains of impulses are repeated at armature 273 of relay 271 in a manner which will be clear, and relay 278 is operated during each train of impulses to short-circuit relay 302 and retard 288. Relay 283 does not release during the setting up of the connection because a locking circuit is completed for it by relay 278 during a train of impulses and by relay 302 between trains of impulses. lVhen the connection has been completely set up or a busy condition encountered however, the circuit for relay 302 is opened and the relay de-energizes, thereby bringing down relay 283 also to establish supervisory conditions. The circuits remain in this condition until the called party replies, whereupon a circuit is completed over the upper speaking conductor tor relay 302 and this at armature 303 connects up retard 305 to conductor 260 and since the dialling key has now been restored. the circuit for relay 254 is completed. This relay upon operating, at armature 255 shortcircuits lamp 256 so as to give the operator answering supervision. It will be noticed that only a single relay such as 302 need be provided in the operators selector, since the question of metering will be determined by the operator herself, and moreover it is desirable that she should always have control of the release of the connection and hence this relay will be arranged to operate in series with a resistance such as is included in the busy circuit. It will be noted also that in case the called party should hang up and should then remove his receiver again before the operator has taken down the connection, he will be able to eatinguisa the supervisory lamp in the cord circuit or flash it if desired so that the attention of the operator may be at tracted. The cam springs 806 are operated in case the switch is rotated to the 11th position on any level and serves to connect up busy tone and intermittent battery, and the effect of this will be to operate the relay 254 intermittently and hence flash the lamp 256. A similar flashing signal is given in case any ofthe other switches taken into use for setting up the connection should be unable to find a free outlet, or if the wanted party should be found busy.

Mention should also be made of the lamp 50 in the first selector, which is provided to enable an attendant to ascertain readily particular conditions oi the connection set up over the switch. It will be seen that as soon as relay 8 operates when the switch is taken into use, a circuit is completed for lamp 50 and it glows steadily until it is extinguished by the operation of armature 4 7 when relay 42 operates. A permanent glow is thus obtained in case a subscriber removes his receiver and omits to dial or in case of a fault on the line setting up similar conditions; hence it the attendant notices that a lamp remains lighted for an undue length of time, he will take steps to investigate the trouble. The other case in which the services of the attendant might be required is that of socalled blocked calls in which the called party has hung up but not the calling party, shoe in such a case the called party would be prevented from extending calls himself. Under these conditions however, relay 28 will remain locked up over its lower winding while relay 33 will release. Hence the circuit of the lamp will be completed from earth, armature 30 and its front contact, armature 3e and its back contact and lamp 50 to battery so that an indication is given.

What I claim as new and desire to secure by Letters Patent is 1. In an automatic telephone system in which the impulses for setting the automatic switches are generated by opening and closing a bridge across the two talking conductors including a source of potential and are received in any switch by a receiving device bridged across the two talking conductors independent of a local source of potential, means for subsequently controlling supervision over each of the talking conductors independent of the other.

2. In an automatic telephone system in which impulses for operating automatic switches are transmitted from a first repeater to a second repeater over the two talking conductors of a connecting trunk line in series and are transmitted from the second repeater to automatic switching mechanism, a line relay included in the second repeater to receive the impulses from the first repeater, and means in the second repeater effective after all the impulses have been repeated to disconnect said line relay from the circuit in series with the two talking conductors and to connect it in a circuit including one talking conductor and excluding the other.

3. In an automatic telephone system in which impulses for operating automatic switches are transmitted from a first repeater to a second repeater over the two talking conductors of a connecting trunk line in series and are transmitted from he second repeater to automatic switching mechanism, a line rclay included in the second repeater to receive the impulses from the first repeater, means in the second repeater eiiective after all the impulses have been repeated to disconnect said line relay from the circuit in series with the two talking conductors and to connect it in a circuit including one talking conductor and excluding the other, and circuit arrangements whereby supervisory signals may be transmitted from the second repeater to the first repeater over the said other talking conductor.

In testimony whereof I have signed my name at Liverpool, England, this 23rd day of June, 1926.

ARTHUR JAY RAY. 

